The present invention relates to a motor including a rotor with a consequent-pole structure.
Known rotors of the prior art used in motors may have a consequent-pole structure. Japanese Laid-Open Patent Publication No. 9-327139 describes such a rotor. The rotor includes a rotor core, a plurality of magnets arranged in the circumferential direction of the rotor core, and a plurality of salient poles formed integrally with the rotor core. The magnets function as first magnetic poles. The salient poles function as second magnetic poles and are arranged between adjacent magnets.
In a motor of a normal structure having magnetic poles that are all formed by magnets, when there are an odd number of pole pairs formed by magnets, any magnetic pole separated by 180 degrees from one magnetic pole is a magnet. Thus, the rotor has a preferable magnetic balance. In contrast, in a motor including a rotor having the consequent-pole structure described in the above publication, the salient poles have no constraining force (induction) acting on the magnetic flux. This induces a large amount of the magnetic flux of magnets to the salient poles that have a small magnetic resistance. Thus, in a motor including a rotor having the consequent-pole structure, the rotor is magnetically imbalanced in a radial direction. This increases vibration of the motor.